sounds like it could be a loose spark plug. Get in there and torque them down. If you have a torque wrench the spec is
Spark Plug to Cylinder Head . . . . . 30 Nm (22 ft-lb) (Bentley, page 020-11)
If you need to replace them they are Bosche F7 L DCRs (Bentley, page 020-11)
Also make sure the coil boots are in good shape and not damaged
1995 525iA 250k mi
2006 325i/6 57k mi
2003 350Z 88k mi
Last edited by Monsignor; 01-11-2013 at 11:05 AM.